1. Field of the Invention
The present invention relates to a cam mechanism for a lens barrel which is provided with a cam ring for moving a linearly guided ring member of the lens barrel.
2. Description of the Related Art
Photographing lens barrels are often provided with a cam mechanism using a cam ring wherein the cam ring is provided on an inner peripheral surface thereof with a set of cam grooves while a set of cam followers which are respectively engaged in the set of cam grooves are formed on a linearly guided ring member which is linearly guided along a photographing optical axis so that the linearly guided ring member moves between a ready-to-photograph position and an accommodation position (retracted position). Therefore, each cam groove of the cam ring has a photographing section for moving the linearly guided ring member to the ready-to-photograph position and an accommodation section for positioning the linearly guided ring member to the accommodation position, in which no pictures are taken.
Such cam grooves of the cam mechanism are conventionally formed on the cam ring so that the opposite ends of each cam groove are formed as closed ends, i.e., so that either end of each cam groove is not open at the front end or the rear end of the cam ring. Even in the case where each cam groove is provided at the front end or the rear end of the cam ring with a cam follower insertion opening through which the associated cam follower is inserted into the cam groove, each of the aforementioned photographing section and the aforementioned accommodation section is shaped so that both the opposite ends thereof are closed (i.e., so that each of the front cam surface and the rear cam surface in each cam groove can be in contact with the associated cam follower).
However, the inventors of the present invention have found that the above described conventional cam groove design, which forms each cam groove as a closed cam groove, restricts the reduction in axial length of the cam ring, thus preventing the length of the lens barrel from being minimized.